Black Hole
Space & Structure
In one sentence
A black hole is a region of space where gravity is so intense that, once anything crosses its boundary—the event horizon—not even light can escape.
A simple example
Imagine a waterfall so powerful that, after crossing its edge, even the fastest swimmer could never return. A black hole’s event horizon is a one-way boundary: once crossed, every possible path leads farther inward.
Go Deeper
Black holes can form when very massive stars collapse, and much larger black holes inhabit the centers of many galaxies. Their gravity curves spacetime so strongly that crossing the event horizon makes escape impossible. Matter falling toward a black hole can heat up and shine brightly before crossing that boundary. According to quantum theory, black holes should also release an extremely faint glow called Hawking radiation and gradually lose energy, although this radiation has not yet been directly detected from an astrophysical black hole. What happens at the deepest interior remains one of physics’ greatest unanswered questions.